Sedimentology and paleontology of a tsunami deposit accompanying the great Chilean earthquake of February 2010

TitleSedimentology and paleontology of a tsunami deposit accompanying the great Chilean earthquake of February 2010
Publication TypeJournal Article
Year of Publication2011
AuthorsHorton BP, Sawai Y, Hawkes AD, Witter RC
JournalMarine Micropaleontology
Volume79
Issue3-4
Pagination132-138
Date Published05/2011
Keywords2010 Chile earthquake, Microfossils, Tsunami
Abstract

At Pichilemu, in the northern third of the rupture area of the moment magnitude scale (Mw) 8.8 2010 Chile earthquake, deposits of the tsunami accompanying the earthquake consist of a lower layer of medium to fine sand (mean grain size of 200 μm) containing rock clasts, overlain by a thin, silty, very fine sand (mean grain size of 125 μm) layer. Based on a sedimentological model, most (90%) of the deposit is finer than 401–408 μm suggesting tsunami flow velocities were between 7 m/ s and 13.5 m/ s. Ostracods were common in the upper layer along with a small number of broken benthic foraminifera and a single planktonic foraminifera. Diatoms were abundant throughout. Species assemblages represent a mixture of diatoms from differing environments, life forms and substrate preferences. We attribute the mixed assemblages to turbulence within the water column during tsunami inundation, with erosion of beaches and salt marshes followed by redeposition of sand and mud inland. Breakage of fragile diatom valves in the lower layer may also support transport by turbulent flow. A higher abundance of diatom species with mud substrate preferences in the upper layer implies a decrease in flow velocity from lower to upper layers.

URLhttp://www.sciencedirect.com/science/article/pii/S0377839811000193
DOI10.1016/j.marmicro.2011.02.001